Now let’s look at some “yes” scenarios. These are the ones where the virtual machine is built under Virtual PC or Virtual Server initially. If you take a VHD image and create a new VM in Hyper-V usng that VHD and simply boot it, yes, it will be fine. If you do not install the Integration Components and subsequently take the VHD back to Virtual PC or Virtual Server, yes, it will also boot fine.

Guess you also want to know what will not work. So go and check John's post.